1. Field of the Invention
The present invention relates to a non-volatile memory device and a cross-point memory array including the same, and more particularly, to a non-volatile memory device and a cross-point memory array including the same which have a diode characteristic enabling the non-volatile memory device and the cross-point memory array including the same to operate in a simple structure, without requiring a switching device separately formed so as to embody a high density non-volatile memory device.
2. Description of the Related Art
It is preferable that a semiconductor memory device has a lot of memory cells formed in each unit region so as to have high integration, has high operating speed, and can operate with low power. For this purpose, many researches have been conducted, and many kinds of memory devices have been developed.
In general, the semiconductor memory device includes a lot of memory cells which are connected in a circuit. In the case of a dynamic random access memory (DRAM) which is a representative semiconductor memory device, a unit memory cell is generally comprised of a switch and a capacitor. The DRAM is advantageous due to its high integration and high operation speed. However, the DRAM is disadvantageous since it loses all stored data when power is off. On the other hand, a flash memory is a representative example of a non-volatile memory device which can retain stored data when power is off. The flash memory is non-volatile in contrast with a volatile memory, but the flash memory is disadvantageous due to its low integration and low operating speed, compared to the DRAM.
A magnetic random access memory (MRAM), a ferroelectric random access memory (FRAM), a phase-change random access memory (PRAM), a resistance random access memory (RRAM), and the like are examples of the non-volatile memory device for which many researches have been conducted.
The MRAM stores data by using a change of a magnetization direction in a tunnel junction. The FRAM stores data by using ferroelectric polarization. The MRAM and the FRAM respectively have advantages and disadvantages. However, as described above, the MRAM and the FRAM are being researched and developed so as to have high integration, high operating speed, high data retention, and to operate with low power. The PRAM stores data by using a change in a resistance value according to a phase-change of a specific material, and has a structure including a resistor and a switch (transistor). The resistor which is used for the PRAM is a calcogenide resistor. The calcogenide resistor adjusts a forming temperature and becomes a crystalline state or an amorphous state. In general, since a resistance in the amorphous state is higher than the resistance in the crystalline state, a memory device is formed by using this attribute.
The RRAM uses a characteristic (a resistance change characteristic) in which a resistance value is differed due to an applied voltage. Materials showing such a resistance change characteristic are an extraordinary magnetoresistive material such as Pr0.3Ca0.7MnO3 (PCMO), a binary transition metal oxide, a ferroelectric material, a programmable metallization cell (PMC) material on which a material having a high ion mobility is doped, and the like. Examples of the binary transition metal oxide are ZnO, TiO2, Nb2O5, ZrO2 or NiO, etc.
Meanwhile, in order to form the RRAM having a cross-point array structure, a separate switch structure is required so as to write and read information without interference from an adjacent cell. Thus, in general, a memory device has a structure which is connected to a transistor structure or a diode structure.